Thermal diffusivity is a measurement of the ability of a material to conduct thermal energy relative to its ability to store thermal energy. It may be calculated using the material's thermal conductivity (W/(m·K)) divided by its density (kg/m3) and specific heat capacity (J/(kg·K)). As an example, heat moves rapidly through a substance with high thermal diffusivity because the substance conducts heat quickly relative to its volumetric heat capacity.
Thermal diffusivity may be measured using the “flash” method. This involves heating a sample of material (e.g., a strip or cylindrical sample, etc.) with a short energy pulse (e.g., heat source such as a light beam, laser, etc.). The temperature change in the sample may then be measured over time.
The assignee of the present application is a manufacturer of flash systems used to measure thermal diffusivity. One such system is the LFA 447 NanoFlash®. The LFA 447 is a compact measuring system, with the flash lamp, sample plate, and sensor vertically arranged. Samples of material are placed on an automatic sample changer, which can test up to four samples. Using the LFA 447, a first side of a sample of material is heated by a short light pulse. The resulting temperature rise on the sample's other side is measured using an infrared sensor. By analyzing the resulting temperature-versus-time curve, the thermal diffusivity of the sample of material can be determined.
U.S. Pat. Pub. 2014/0036955 to Brunner discloses a device and method for the photothermic investigation of a sample. It uses a sample holder that is movable in relation to a fixed optical excitation/detection path. U.S. Pat. No. 6,273,603 to Cheindline discloses a measuring head for use in radiant energy flash measuring of the thermal diffusivity of samples. It uses a movable sample holder and a fixed side view detector, which requires a mirror moving in three coordinates to reflect light from the sample. Neither of these references, the contents of which are incorporated by reference in their entirety, discloses use of a mask.
However, known systems for measuring thermal diffusivity have a number of deficiencies, including that they only provide for testing a sample through the thickness of the sample. Therefore, it would be beneficial to have a superior system and method for measuring 3D diffusivity.